The number of operating partnership units of CyrusOne LP sold during the period.

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Costs incurred for exploring strategic alternatives for our Wireless business, costs incurred for agreement to sell our Wireless spectrum licenses and certain other assets and exploring monetization of our CyrusOne investment; legal and consulting costs incurred to restructure legal entities in preparation for the IPO of the common stock of CyrusOne Inc. and to prepare CyrusOne to be a real estate investment trust; and legal and consulting costs incurred to investigate acquisition opportunities.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount of gain (loss) on sale or disposal of an equity method investment.

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Gross amount of debt extinguished.

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The charge against earnings resulting from the write down of long lived assets other than goodwill due to the difference between the carrying value and lower fair value.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

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Quarterly Financial Information (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012
Selected Quarterly Financial Information [Abstract]
Revenue	$ 308.3us-gaap_SalesRevenueNet	$ 327.5us-gaap_SalesRevenueNet	$ 319.9us-gaap_SalesRevenueNet	$ 322.5us-gaap_SalesRevenueNet	$ 308.4us-gaap_SalesRevenueNet	$ 310.8us-gaap_SalesRevenueNet	$ 312.0us-gaap_SalesRevenueNet	$ 325.7us-gaap_SalesRevenueNet	$ 1,278.2us-gaap_SalesRevenueNet	$ 1,256.9us-gaap_SalesRevenueNet	$ 1,473.9us-gaap_SalesRevenueNet
Operating income	7.3us-gaap_OperatingIncomeLoss	16.0us-gaap_OperatingIncomeLoss	35.6us-gaap_OperatingIncomeLoss	56.9us-gaap_OperatingIncomeLoss	40.1us-gaap_OperatingIncomeLoss	57.7us-gaap_OperatingIncomeLoss	46.8us-gaap_OperatingIncomeLoss	19.2us-gaap_OperatingIncomeLoss	115.8us-gaap_OperatingIncomeLoss	163.8us-gaap_OperatingIncomeLoss	270.1us-gaap_OperatingIncomeLoss
Net income (loss)	(18.3)us-gaap_NetIncomeLoss	(27.3)us-gaap_NetIncomeLoss	114.2us-gaap_NetIncomeLoss	7.0us-gaap_NetIncomeLoss	(28.1)us-gaap_NetIncomeLoss	9.3us-gaap_NetIncomeLoss	0.8us-gaap_NetIncomeLoss	(36.7)us-gaap_NetIncomeLoss	75.6us-gaap_NetIncomeLoss	(54.7)us-gaap_NetIncomeLoss	11.2us-gaap_NetIncomeLoss
Earnings Per Share, Basic	$ (0.10)us-gaap_EarningsPerShareBasic	$ (0.14)us-gaap_EarningsPerShareBasic	$ 0.54us-gaap_EarningsPerShareBasic	$ 0.02us-gaap_EarningsPerShareBasic					$ 0.31us-gaap_EarningsPerShareBasic
Earnings Per Share, Diluted	$ (0.10)us-gaap_EarningsPerShareDiluted	$ (0.14)us-gaap_EarningsPerShareDiluted	$ 0.53us-gaap_EarningsPerShareDiluted	$ 0.02us-gaap_EarningsPerShareDiluted
Basic and diluted earnings (loss) per common share					$ (0.15)us-gaap_EarningsPerShareBasicAndDiluted	$ 0.03us-gaap_EarningsPerShareBasicAndDiluted	$ (0.01)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.19)us-gaap_EarningsPerShareBasicAndDiluted	$ 0.31us-gaap_EarningsPerShareBasicAndDiluted	$ (0.32)us-gaap_EarningsPerShareBasicAndDiluted	$ 0.00us-gaap_EarningsPerShareBasicAndDiluted
Effect of Fourth Quarter Events [Line Items]
Restructuring charges		9.0us-gaap_RestructuringCharges							15.9us-gaap_RestructuringCharges	13.7us-gaap_RestructuringCharges	3.4us-gaap_RestructuringCharges
Gain on sale of CyrusOne equity method investment			192.8						192.8	0	0
Impairment of assets, excluding goodwill									(12.1)us-gaap_OtherAssetImpairmentCharges	0us-gaap_OtherAssetImpairmentCharges	(14.2)us-gaap_OtherAssetImpairmentCharges
Equity Method Investment Sold, Partnership Units			16.0
Transaction costs		3.0cbb_Transactioncosts							4.4cbb_Transactioncosts	1.6cbb_Transactioncosts	6.3cbb_Transactioncosts
Debt Instrument, Redemption Price, Percentage					104.125%
Gains (Losses) on Extinguishment of Debt									19.6	29.6	13.6
Senior Subordinated Notes due 2018 [Member]
Effect of Fourth Quarter Events [Line Items]
Extinguishment of Debt, Amount									325.0
Debt Instrument, Redemption Price, Percentage		104.375%
Gains (Losses) on Extinguishment of Debt									19.4
Senior Notes due 2020 [Member]
Effect of Fourth Quarter Events [Line Items]
Extinguishment of Debt, Amount									22.7		91.1	91.1
Gains (Losses) on Extinguishment of Debt									0.2
Senior Notes due 2017 [Member]
Effect of Fourth Quarter Events [Line Items]
Extinguishment of Debt, Amount										500.0
Debt Instrument, Redemption Price, Percentage					104.125%
Gains (Losses) on Extinguishment of Debt					29.6
Wireless [Member]
Selected Quarterly Financial Information [Abstract]
Revenue									132.8	201.5	241.8
Operating income									(66.3)	18.2	51.2
Effect of Fourth Quarter Events [Line Items]
Restructuring charges			6.4						16.3	0.2	1.6
Impairment of assets, excluding goodwill									7.5		0.4
Transaction costs									$ 3.2